Gyrocompass

ABSTRACT

A pendulous gyrocompass of the type in which the rotor case if floated and the motor for driving the rotor in the rotor case is supplied with electrical power through a pair of speciallyconstructed electrically-conductive azimuth gimbal pivots of the needle-bearing type. The other gimbals in the gimbal support system may be relatively lower-grade bearings, with conventional arrangements for passing the motor current through or around them. The resultant gyrocompass may be of small size and low cost, and does not require servo&#39;&#39;s, pickoffs, torquers, sliprings, internal power supplies or other specialized compensating or correcting devices, yet provides an accuracy suitable for many applications.

United States Patent [1 1 Dec. 25, 1973 Taylor GYROCOMPASS [75]Inventor: Marvin Taylor, Plainview, NY.

[73] Assignee: AMBAC Industries, Incorporated,

Garden City, NY.

[22] Filed: May 12, 1971 [2]] Appl. No.: 142,584

[52] US. Cl. 33/327 [51] Int. Cl G0lc 19/38 [58] Field of Search 33/324,325, 326, 33/327 [56] References Cited UNITED STATES PATENTS 2,797,5817/1957 Carter 33/327 X 875.036 12/1907 Ach 33/324 X- 1,739,251 12/1929Mills 33/324 UX 2,677,194 5/1954 Bishop 33/325 UX 1,625,361 4/1927Henderson.... 33/324 UX 1,891,856 12/1932 Williams 33/324 UX FOREIGNPATENTS OR APPLlCATlONS 146,372 5/1921 Germany 33/327 ABSTRACT Apendulous gyrocompass of the type in which the rotor case if floated andthe motor for driving the rotor in the rotor case is supplied withelectrical power through a pair of specially-constructedelectrically-conductive azimuth gimbal pivots of the needle-bearingtype. The other gimbals in the gimbal support system may be relativelylower-grade bearings, with conventional arrangements for passing themotor current through or around them. The resultant gyrocompass may beof small size and low cost, and does not require servos, pickoffs,torquers, sliprings, internal power supplies or other specializedcompensating or correcting devices, yet provides an accuracy suitablefor many applications.

3 Claims, 15 Drawing Figures PATENTED UECZ 5 I975 FIGI.

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INVENTOR MARVIN TAYLOR ATT VS.

.GYROCOMPASS BACKGROUND OF THE INVENTION This invention relates toimprovements in gyrocompasses, and particularly to improvements whichresult in greater simplicity and lower cost of pendulous gyrocompassesof the floated-case type.

Gyrocompasses have long been known in the art, and utilized very widelyfor purposes of marine and terrestrial navigation'and the like. They arein fact standard on nearly all large ships, and serve the function ofindicating the direction to the polar axis of the earths rotation. Inthe usual form, the gyrocompasses utilizes, in effect, a pendulouslymounted gyro rotor which, when set spinning, tends to maintain thedirection of its spin axis fixed in inertial space. lf at any time thespin axis is not pointing toward polar north, the rotation of the earthcarrying the gyrocompass will result in an appararent raising of one endof the spin axis, although this axis is actually tending to remain fixedin direction in inertial space. Due to the pendulosity of the device, atorque will be exerted on the rotor in the direction to urge it backtoward its apparently horizontal position with respect to the earth.However, due to the wellknown precessional properties of a gyroscope,the resultant torque will in fact cause the spin axis to move insteadabout the vertical toward a position in which the spin axis pointsnorth. After some initial oscillation, the. spin axis will point north,and will continue to do so despite rotation of the earth.

Theprincipal advantage of the gyrocompass over the magnetic compass isthat it is not dependent upon the direction of the earth's magneticfield, and hence is not sensitive to distortions of that field due toadjacent metal, such as the metal structure of a ship or other vehicle,nor to local or temporal variations in the earths magnetic field, nor tostray magnetic fields of varying strengths. The gyrocompasses nowavailable are generally very complex devices costing many thousands ofdollars. While they are able to provide high accuracy, they maytypically employ any or all of a number of relatively complicating,expensive devices, such as servos pickoffs, torquers, sliprings,internal power supplies, speed correctors, temperature controllers, etc.

One of the problem areas resulting in such complexity relates to theneed for supplying electrical power to drive the motor operating therotor. Merely connecting wires directly from a base-supported powersupply to a motor supported on the gimbal assembly will normally resultin excessive inaccuracy due to the torques exerted by the electricalleads, and in many cases this will also interfere with completely full,free, azimuth rotation of the spin axis, such as is desirable to enableoperation for any heading of the vehicle carrying the gyrocompass.

Attempts have been made to overcome this by including an electricalpower source, such as a battery, within the rotor case itself, but thiscreates additional problems relating to the longevity and voltageregulation of the power source, as well as problems related to providingfor replacement of the power source from time to time. One of the moresophisticated types of gyro compasses available attempts to overcomesome of these problems by utilizing pickofi's which sense the azimuthangle deviation of the rotor case with respect to a surrounding outercase, and employs torquers and servos to cause the outer case to followthe rotor case slowly in angular position about the azimuth axis, withthe result that leads extending between the outer case and the gyrorotor will not be appreciably flexed during operation, and hence willnot exert appreciable torques on the rotor, and will not be wound up bycomplete azimuth rotations of the gyro. The compass bearing is thendetermined by measuring the angular position of the outer case. Not onlyis such an arrangement expensive, but, due to its inherent complication,it tends to be unreliable and unstable, at least to some degree, andintroduces more possibilities of malfunction. In some gyrocompassessliprings have been utilized as a way of supplying the necessaryelectrical power across the various gimbals in the gimbal suspensionbut, particularly whenever relatively large numbers of such electricalconnections are required, the sliprings exert undue frictional restraintand hence exert disturbing torques on the rotor.

Accordingly, it is an object of the invention to provide a new anduseful gyrocompass.

Another object is to provide such a gyrocompass which is of low cost andsize, and yet of an accuracy adequate for many purposes.

It is also an object to provide such a gyrocompass which does notrequire servos, pickoffs, torquers, sliprings or batteries within therotor casing.

BRIEF SUMMARY OF THE INVENTION In accordance with the invention, theseand other objects are achieved by the provision of a pendulousgyrocompass comprising a floated rotor case which contains gyro rotormeans and electric motor means for spinning said rotor means about itsspin axis, the gyrocompass also comprising azimuth axis gimbal meanssupporting said rotor case and permitting it to turn about the azimuthaxis of the gyrocompass, and a pair of separate current-conductive pathsfor supplying operating current to the motor means, wherein the azimuthaxis gimbal means comprises a pair of azimuth gimbal pivots the bearingsurfaces of each of which are electrically conductive and positioned onthe azimuth axis, the bearing surfaces of each of these pivots beingelectrically isolated from those of the other of said pivots, and one ofthe current conductive paths extending through the bearing surfaces ofone of said pivots and the other of said current conductive pathsextending through the bearing surfaces of the other of the pivots.

Preferably the two opposed bearing surfaces of each of the pivots arespring-tensioned against each other, and preferably one element of eachof the pivots is a pivot pin having at one end a hard metal bearingsurface symmetrical about the azimuth axis and of small radius ofcurvature, while the other element of each of the pivots is a pivot seatof hard metal in the form of a depression symmetrical about the azimuthaxis. The above-mentioned spring-tensioning is preferably provided by acorresponding pair of cantilevered leaf springs which not only urgetogether the bearing surfaces of the pair of pivots but also serve asthe positioning means for the azimuth axis of the gyrocompass.

It has been found that this type of gyrocompass is substantially lesssensitive to undesired torques about its horizontal axes than to thoseabout its azimuth axis, and that simple and inexpensive means ofconnection may be employed for supplying the electrical motor poweracross the gimbals of the horizontal axes; for example, the electricalcurrent may be passed through ball-bearing supports, through any ofvarious forms of rubbing or rolling contacts, or even through flexiblewires of small diameter. The gyrocompass is substantially more sensitiveto undesired torques around its azimuth axis, and the preferred form ofazimuth gimbal axis support, comprising pivots turning about and on theazimuth axis itself, provide a low-friction bearing arrangement in whichsuch restraining frictional forces as do develop between the pivotsurfaces are on, or so close to, the azimuth axis as to exert verylittle restraining torque. In the arrangement of the invention, theseazimuth pivots themselves are used to supply the motor current, withoutintroducing disturbing torques about the azimuth axis due to the meansfor supplying the motor current across the azimuth gimbal. Because ofthe floatation of the motor case, the load on the azimuth pivots ismaintained very small soas to reduce any remaining frictional restraintsabout the azimuth axis. Positive electrical contact and definitepositioning of the rotor case in the vertical direction is assured byuse of the spring tensioning arrangement. Preferably the lower of thesespring-tensioning arrangements which urges the rotor case upwardly isarrested in its upward motion by appropriate stop means, the upwardurging force being sufficient to overcome the downward urging force dueto the other spring means, thereby assuring a definite vertical positionof the rotor case during normal operation, but providing the desiredresilience to assure continuous electrical contact for accommodatingsudden random or accidental accelerations along the azimuth axis withoutharm to the gyrocompass or its azimuth pivots.

BRIEF DESCRIPTION OF FIGURES These and other objects and features of theinvention will be more readily understood from-a consideration of thefollowing detailed description, taken in connection with theaccompanying drawings, in which:

FIG.1 is a schematic elevational view, partly in section, illustratingone form of the invention;

FIG. 2 is a sectional view taken along lines 2-2 of FIG. 1;

FIG. 3 is a vertical sectional view of a form of the invention. shown ingreater detail than in FIG. 1;

FIG. 4 is a sectional view taken along lines 4-4 of FIG. 3;

FIG. 5 is a sectional view taken along lines 5-5 of FIG. 4;

FIG. 6 is a sectional view taken along lines 6-6 of FIG. 3;

FIG. 7 is an enlarged fragmentary view of a portion of the apparatus asshown in FIG. 4, with portions omitted;

FIG. 8 is an enlarged fragmentary view of a portion of the apparatus asshown in FIG. 3;

' FIG. 9 is a sectional view taken along lines 9-9 of FIG. 3;

FIG. 10 is a schematic elevational view, partly in section, showinganother form of embodiment of the invention;

FIG. 11 is a sectional view taken along lines 11-11 of FIG. 10;

FIG. 12 is a plan view of the apparatus of FIG. 10;

FIG. 13 is a sectional view taken along lines 13-13 of FIG. 11;

FIG. 14 is a side view of one physical form of realization of theapparatus of FIG. 10; and

FIG. 15 is a front elevational view of the apparatus of FIG. 14.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS Referring first to theembodiment of the invention illustrated schematically in FIGS. 1 and 2,in which the parts are not necessarily to scale and various unnecessarydetails have been omitted in the interest of clarity of exposition,there is shown a gyro rotor 10a, 10b in this instance made in two partswhich are mounted respectively on the two motor shafts 12a and 12bextending from opposite ends of the electric motor 14, so that when themotor 14 is supplied with electrical operating power the gyro rotor isspun rapidly about the spin axis S. The motor 14 is held by a rotormount 16 encircling the motor, and the motor mount in turn is rotatablysupported for easy turning about the tilt axis T by means of the opposedtilt axis pivots l8 and 20. The tilt axis pivots 18, 20, in turn arefixed to a gimbal ring 22 supported at opposite sides thereof by a pairof pivots 24 and 26 for easy turning about an axis X disposed at rightangles to the tilt axis and to the azimuth axis A. The latter pivots,24, 26 are affixed to the interior of the sealed rotor case 28 by thesupports 30, 32. A pendulous weight 34 is affixed to the motor mount 16to render the motor and the rotor assembly pendulous about the two axesT and X. Appropriate damping means for damping out gyrocompassingoscillations about the azimuth axis may be provided in the form of thefour liquid-containing chambers 31 and appropriate interconnectingtubing such as 33, which may be filled with a heavy liquid such asmercury to provide damping in known manner.

The rotor case 28 is suspended in substantially neutral buoyancy withinthe liquid 35, which may be a conventional gyro floatation liquid of lowviscosity, low volatility, and high electric resistivity, held within anouter casing 36. By appropriate selection of the size of the rotorcasing with respect to the weight of its contents and of the partsaffixed thereto, and with respect to the density of the floatationliquid, the rotor casing and the external elements affixed thereto arecaused to have little substantial tendency to sink or rise within theliquid over a substantial temperature range, and are substantiallyweightless.

The arrangement and construction thus far described with reference toFIGS. 1 and 2 may be generally conventional in form. In accordance withthe invention, the rotor case is supported and positioned, andelectrical operating currents applied to the motor 14, in the manner nowto be described.

A metal shaft 38 affixed to the top of rotor case 28 extends upwardalong the azimuth axis and carries at its upper end an upwardly-directedpivot pin 40 ending in an upwardly-directed conical point or end ofsmall radius and of hard material such as steel. The upward tip of pivotpin 40 is seated in the bottom of a generally conical concavity 42 inthe pivot seat 44. Seat 44 is of hard, electrically-highly-conductivematerial such as a hardened precious metal alloy. Pin 40 has a radius atits tip that is considerably smaller than the radius at the bottom ofconcavity 42. The pivot seat 44 is retained in the outer end of acantilevered leaf spring 46, the other end of which is secured to asuitable mount 48 affixed to a projection 50 on the interior of theouter casing 36. Spring 46 is pre-tensioned downwardly so as to urgepivot pin 40 an d pivot seat 44 against each other.

In the form shown, the pivotseat has an upwardlyextending portion 49 ofreduced diameter extending through an opening in the leaf spring, towhich upper portion,,an appropriate electrical lead 54 is conductivelysecured. The latter lead exits from the outer casing by way of anappropriate bushing 56 and, during operation of the gyrocompass, will besupplied with operating current from one terminal of the electricalsupply source. As an example, this may be the ground terminal of thesupply source and, due to the electrically conductive path through thepivot seat, pivot pin and shaft 38 and the rotor casing 28, the supports30, 32 are maintained at the potential of the lead 54, in this exampleground.

At its bottom'end, the rotor case 28 is supported by another azimuthpivot comprising pivot pin 60 and pivot seat 62, the latter pivot seatbeing supported in turn at the outward end of the cantilever spring 64mounted on the outer casing 36. The azimuth pivot below the rotor casingmay be like that described previously for use above the rotor casing,with the exception that both the pivot pin 60 and the pivot seat 62 areinsulated from the rotor case, and from the outer casing, by means ofinsulating supports 66 and 68 respectively. In this example the rotorcase 28, the shaft 38, and the upper and lower azimuth pivots constitutethe azimuth gimbal means of the gyrocompass.

To supply electrical motor power across the lower pivot, the externalmotor lead 74 is passed through a bushing 72 in the outer casing andconductively connected to the pivot seat 62, and a lead 74A isconductively connected from the pivot pin 60 through an appropriatesealing bushing 76-to the interior of the rotor case. The latter lead74A may then be connected to the ungrounded or hot" supply terminal ofthe motor 14 in any convenient manner which will not introduce unduerestraint on the gyro rotor, for example, by insulated leads passingthrough and along the horizontal support axes for the rotor, or even bya direct flexible wire connection. In this way, again, the conductivepath for supplying current to operate the motor is passed through thepivoton the azimuth'axis, thereby minimizing undesired torques about theazimuth axis. This pivot arrangement again also provides a very lowfriction support for permitting free turning of the rotor case inazimuth, and positions the rotor case vertically along the azimuth axisas well as centering it in position on a horizontal plane due to thesymmetrical concavity forming the pivot-seat bearing surface.

As shown, a stop 78 is preferably secured to the outer casing in aposition to arrest the upward motion of the lower pivot during normaloperation, the lower cantilever spring 64 being biased upwardlysufficiently strongly to cause the pivot to remain urged against thelower surface of the stop. This provides a definite vertical positioningof the'rotor case under conditions of normal operation, while at thesame time providing sufficient spring tension to maintain the azimuthbearing surfaces in appropriate contact under low load, and to assurethe desired electrical contact by which the motor power is suppliedacross the azimuth pivots. For example, utilizing the rotor casearrangement shown in FIG. 1, the lower spring 64 may exert an upwardspring force of about 2 ounces against the stop 78, and the upper spring46 may exert a downward force of about 1 ounce, providing the desiredazimuth axis centering, vertical positioning and electrical contact.

Referring now to FIGS. 3-9 which show in more detail a representativeembodiment of the invention shown schematically in FIG. 1, partscorresponding to those of FIG. 1 are indicated by correspondingnumerals.

There are again employed the outer casing 36 in this case provided witha top cover 80 which is screwed on to the upper part of the casing; therotor case 28, in this example in the form of a metal cylinder; theshaft 38 secured to a bushing on the top of the rotor case 28 by meansof a bolt 84; the upper and lower pivot pins 40 and 60 respectively; theupper and lower pivots seats 44 and 62 respectively; the upper and lowercantilever springs 46 and 64 respectively; the motor 14; the motor mount16 with the pendulous weight 34 at the bottom end thereof; the dampingarrangement consisting of the four chambers such as 31 and theinterconnecting tubing 33; the stop 78 mounted by screws such as 85 on aboss 88 secured to the bottom of the interior of the outer casing; thetwo-part rotor 10a, 10b; the leads 74 and 54 for supplying electricaloperating power to the motor, which in this embodiment enter through anappropriate bushing 86 in the outer casing cover 80; the gimbal ring 22;the ball-bearing pivots 24, 26 for turning about the X axis; and severaladditional details of construction preferably utilized in thisembodiment and to be described hereinafter.

As is shown particularly clearly in FIG. 5, the tilt axis is provided inthis example by knife-edge bearings 18, 29, the knife edges serving tosupport the motor and rotor assembly for tilt motion thereof. However,other arrangements such as ball-bearing pivots may be utilized for thetilt pivots if desired, as in the case of the pivots 24, 26.

The floatation liquid level, as shown in FIG. 3, is above the rotor case28 but below the liquid baffle structure 94. The latter baffle structureis preferably used to impede the flow of the liquid into the regionoccupied by the shaft encoder 96, when the gyrocompass is tilted. Theshaft encoder 96 may be of conventional form, including for example alight source assembly 98 and a photocell assmbly 100 cooperating with anoptically-coded disc 102 secured to shaft 38. Appropriate leads from theexterior of the outer casing are passed through bushing 86 to supply thelamps in the light source assembly, and appropriate output leads fromthe photocell assembly 100 pass outwardly through the bushing 86. Thevoltages on the latter set of photocell leads provide a direct externalvoltage indication of the angular position of the rotor case 28 withrespect to the outer casing, and may be utilized to operate any exteriorangle-indicating device or to supply information to a computer, forexample.

Also shown in this example is a slewing motor having motor leads 112connected to an external source of power by way of the bushing 86 forrotating a spiral spring 114 when an external operator's switch isactuated, the spring supporting at its upper end a weight 116. Whenmotor 110 is operated and spring 114 and weight 116 caused to spin, theweight 116 executes a wobbling circular motion, departing from the axisof the spring sufficiently to strike the periphery of the disc 118secured to the shaft 38, causing the latter disc to turn on onedirection of rotation; when the direction of the motor 110 is reversedby means of the external control, the circular motion of the weight 116is in the opposite direction and tends to turn the disc 118 in theopposite sense. In this way the rotor case 28 and its contents may bemoved rapidly to a desired angular position with respect to the outercasing at a more rapid rate than would be the case if one merely waitedfor the normal gyro precessional motion to occur.

The particular manner of supplying the motor electrical motor power fromthe exterior will now be outlined. Lead 54 from the exterior of casing36 passes through the bushing 86 to the screw terminal 120 and then to aconnection point 122 on the pivot seat 44. From here the conductive pathextends through the pivot pin 40 and the conductor shaft 38 to the rotorcase 28, the thence through the metal supports 30, 32 to the gimbal 26.Although conduction through this gimbal may be by way of theball-bearing assembly contained therein, it is preferred in this exampleto include a conductive pin 124 (see especially FIG. 6) aligned with theX axis of that gimbal, which at its inner end makes sliding electricalcontact with a blade 128 secured to the conductive gimbal ring 22.Again, although conduction through the gimbal ring 22 may be relied uponin this example lead 54A is employed which extends quarter way aroundthe gimbal 22 to the tilt axis (see especially P16. 4 and FIG. 7), whereit connects to a spring 130 which contacts and urges outwardly aconductive ball 132, thereby urging the latter ball against a conductiveplate 134 to provide a rolling conductive contact across the tilt axis.The plate 134 is in turn connected by the lead 548 to the motor tosupply the necessary operating power. The current path just described,as mentioned above, may reprsent the ground connection for the motor.

The other, or hot conductive path for supplying currrent to the motorstarts with external lead 74, which passes downwardly to make electricalcontact at 142 with the lower pivot seat 62. The insulator bushing 68provides electrical insulation from the spring 64. The conductive paththen extends to the pivot pin 60, which is electrically insulated fromthe rotor case 28 by the insulating washer 66. The lead 74A then extendsfrom pin 60 around the outside of the rotor case to the sealedfeed-through 168 and thence to the X-axis pivot 24. The lead with itssurrounding insulation extends along the X axis through this pivot andthrough the gimbal ring 22, and is exposed at its outer end to form asliding contact with the blade 170 mounted in insulating fashion on thegimbal ring 22. From the blade 170, the lead 74C then extends quarterway around the gimbal ring 22 to the tilt axis and then, as shown inFIG. 7, makes contact to a metal slug 174, insulated from itssurroundings by the insulating bushing 176. The slug 174 is in contactwith the ball 178, which is adapted to contact the disc 180 mounted onthe motor side of the tilt axis. From the disc 180 the lead 74D thenextends to the hot" terminal of the motor.

FIGS. through illustrate another embodiment of invention utilizing thesame type of azimuth axis pivot for azimuth axis support and for thesupply of motor current to the interior of the floated rotor case, bututilizing a different gimbal support system and a different arrangementfor providing output indications of azimuth angle. In particular, FIGS.10-13 show schematically a type of floated rotor-case gyrocompasscomprising a spin motor 200, a two-part rotor 202a, 202b mounted to bespun by the motor about the spin axis; a motor-support 208 having apendulous portion 210 for making the motor and rotor assembly pendulousabout a tilt axis provided by the tilt pivots 214 and 216, which may,for example, be ball-bearing pivots. However, in this case, the rotorcase is a spherical metal shell 224 and the motor and rotor assemblycontained therein is fixed to the interior of the rotor case, the rotorcase and the motor and rotor assembly being mounted as a unit on thetilt axis bearings. A suitable damping arrangement comprising liquidchambers such as 225 and interconnecting tubes such as 228 is provided,also as a part of the unitary assembly within the rotor case.

The tilt axis pivots are mounted on the generallyvertical gimbal ring230, on which the azimuth pivot pins 232 and 234 are provided, lyingalong the azimuth axis on opposite sides of the vertical gimbal ring.The azimuth pivot seats 240 and 242 are mounted on respective cantileversprings 246 and 248, which in turn are supported on the interior of theouter casing 250. The outer casing contains a floatation liquid 251. Thelower pivot seat is again electrically isolated from the other metalparts of the gyrocompass, in this case by mounting the lower cantileverspring and the stop 260 on insulating blocks.

The outer casing in this example is mounted upon a generally-horizontalgimbal ring 262, which in turn is free to turn about a roll axis R byvirtue of roll-axis pivots 266 and 268.

The roll-axis pivots in turn are supported on an outermost pitch gimbalring 262 for turning about the pitch axis P by means of pitch axispivots 280 and 282, the latter pivots then being fixed to the supportingsubstructure on which the gyrocompass is mounted. The outer casing isalso rendered pendulous by means of th pendulous weight 288, whereby theazimuth axis is maintained vertical as desired.

Output azimuth-angle indications may be provided by means of a card 289in the form of a ring mounted on the vertical azimuth gimbal ring 230and bearing angle-representative indicia viewable through a transparentwindow 296 in the outer casing blank.

One motor lead is supplied with power from the binding post 297 by wayof the lead 298 which extends through the outer casing to the uppercantilever spring and then through the upper pivot, thereby groundingthe vertical gimbal ring 230 and the metal structure supported thereon,including the rotor case and motor support, to which support the groundconnection of the motor may be connected. The hot" lead extends frombinding post 298 through lead 299 into the outer casing and to the lowercantilever spring, whence the conductive path passes through the lowerpivot pin 234 through the lead 298A to the floated rotor case 224, andthrough the wall of the rotor case to the interior, where it may beconnected to the hot motor lead terminal by lead 298B.

Accordingly, in this configuration also the azimuth gimbal axis meanscomprises the pair of pivots each having their pivot points on theazimuth axis, and again the parts of each pivot are urged lightlytogether by spring means which also act on opposite sides of the azimuthaxis structure, the conical nature of the pivot seats providing lateralpositioning of the azimuth axis. The stop means 260 together withcantilever spring 248 again provides a fixed vertical position for theazimuth axis, as described previously. The rotor case is floated bymeans of the liquid 251 so as to reduce the weight on the lower azimuthpivot to a very small value. There has thereby been provided a simple,small, inexpensive gyrocompass in which accuracies of 2 to 4 degrees areeasily obtained, and which is particularly useful on marine vessels.

FIGS. 14 and 15 show one general physical embodiment of a productembodying such a gyrocompass, wherein there is provided an externalhousing 310 having an on-off power switch 312 for controlling the supplyof current to the gyro spin motor, and supporting and housing agyrocompass like that illustrated schematically in FIGS. 10-13,corresponding parts being indicated by corresponding numerals. The outercasing 250 and the window 296 thereof extend outward from the slantedfront of the external housing, with the azimuth-angle card 289 providingvisible indications of the azimuth angle between the rotor case and theouter casing and hence of the angular deviation from true north of areference line fixed to the external casing and to the vehicle on whichit is mounted. The external generally-horizontal gimbal ring 262 alsoprotrudes somewhat from the slant in front of the external housing, andthe entire exposed front face of the assembly is covered with a clearplastic cover or bubble 326 to protect the gyrocompass from the externalenvironment. Such a unit is inexpensive, small, easy to utilize and yetof sufficient accuracy for many purposes.

While the invention has been described with particular reference tospecific embodiments thereof in the interest of complete definiteness,it will be understood that it may be embodied in a variety of formsdiverse from those specifically shown and described without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

What is claimed is:

1. In a pendulous gyrocompass comprising a floated rotor case containinggyro rotor means and electric motor means for spinning said rotor meansabout its spin axis, said gyrocompass also comprising azimuth axisgimbal means supporting said rotor case and permitting it to turn aboutthe azimuth axis of the gyrocompass, and a pair of separatecurrent-conductive paths for supplying operating current to said rotormeans, the improvement wherein:

said azimuth axis gimbal means comprises a pair of azimuth gimbal pivotsthe bearing surfaces of each of which are electrically conductive andpositioned on said azimuth axis, the bearing surfaces of each of saidpivots being electrically insulated from those of the other of saidpivots, and one of said current-conductive paths extending through thebearing surfaces of one of said pivots and the other of saidcurrent-conductive paths extending through the bearing surfaces of theother of said pivots; and means for spring-tensioning the bearingsurfaces of each of said pivots against each other.

2. The gyrocompass of claim 1, in which said means for spring-tensioningcomprises a pair of cantilevered leaf springs for urging together saidbearing surfaces of said pair of pivots.

3. The gyrocompass of claim 1, wherein said means for spring-tensioningis arranged to spring-bias downwardly the upper pivot of said pair ofpivots and to spring-bias upwardly the lower pivot of said pair ofpivots, and comprising stop means secured to said outer casing limitingthe upward movement of said lower pivot, the upward spring-bias of saidlower pivot being sufficient to maintain said lower pivot in itsupwardmost position as determined by said stop means during normaloperation of said gyrocompass.

1. In a pendulous gyrocompass comprising a floated rotor case containinggyro rotor means and electric motor means for spinning said rotor meansabout its spin axis, said gyrocompass also comprising azimuth axisgimbal means supporting said rotor case and permitting it to turn aboutthe azimuth axis of the gyrocompass, and a pair of separatecurrent-conductive paths for supplying operating current to said rotormeans, the improvement wherein: said azimuth axis gimbal means comprisesa pair of azimuth gimbal pivots the bearing surfaces of each of whichare electrically conductive and positioned on said azimuth axis, thebearing surfaces of each of said pivots being electrically insulatedfrom those of the other of said pivots, and one of saidcurrent-conductive paths extending through the bearing surfaces of oneof said pivots and the other of said currentconductive paths extendingthrough the bearing surfaces of the other of said pivots; and means forspring-tensioning the bearing surfaces of each of said pivots againsteach other.
 2. The gyrocompass of claim 1, in which said means forspring-tensioning comprises a pair of cantilevered leaf springs forurging together said bearing surfaces of said pair of pivots.
 3. Thegyrocompass of claiM 1, wherein said means for spring-tensioning isarranged to spring-bias downwardly the upper pivot of said pair ofpivots and to spring-bias upwardly the lower pivot of said pair ofpivots, and comprising stop means secured to said outer casing limitingthe upward movement of said lower pivot, the upward spring-bias of saidlower pivot being sufficient to maintain said lower pivot in itsupwardmost position as determined by said stop means during normaloperation of said gyrocompass.